Method of making resistors



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Sept. 25, I945. L. STOFFEL METHOD Ol MAKING RESISTORS Filed May 7, 1943 Sept. 25, 1945. L STQFF'EL 2,385,386

' METHOD OF MAKING RESISTORS Filed May 7, 1945 2 Sheets-Sheet 2 7 45 ')FIG.

FIQIG INVENTOR. lame L. .STOHEL Patented Sept. 25, 1945 METHOD OF MAKING RESISTORS Lester L. Stoifel, Lakewood, Ohio, assignor to The Ohio Carbon Company, Cleveland, Ohio, a corporation of Ohio Application May 7, 1943, Serial No. 486,022

- Claims. (C1. 201 .63)

This invention relates to an improved method of manufacturing an electrical resistor, and especially to a method of manufacturing a resistor for use in electric lamp assemblies Where the resistor is enclosed within the lamp base and is connected in the electric circuit of the lamp. More particularly, the invention is concerned with an improved method of manufacturing a resistor for use in electric lamp assemblies of the the type generally shown in my prior Patent No. 2,285,875 issued June 9, 1942, and assigned to The Ohio Carbon Company. These, therefore, are the general objects of the present invention.

The resistors with which this invention is concerned are generally made of a carbonaceous material, and are comparatively small in size so that they may be placed within the base of a lamp. In the past, considerable difficulty has been encountered in making such resistors, particularly in attaching the conductor members or wires to the resistor. This has been due partially to the frangible nature of the resistor, which prevents riveting of the conductor thereto, and to the comparatively small size of the resistor unit, which makes it difficult to secure a good electrical contact between the resistor and the conductor without increasing the size of the resistor or decreasing its current carrying capacity, and at the same time maintain the expense of manufacture at a minimum.

The present invention contemplates the positioning of a plurality of resistor elements in alignment, stretching a continuous strand of wire across the aligned resistors, thereafter securing the Wire to the resistors, and subsequently severing the wire intermediate each resistor. Preferably the wire is secured to each resistor by cement at spaced intervals, and is thereafter severed between each point of securement, thus providing a pair of independent terminals for each resistor. This method of manufacture is both economical and efficient. It adapts itself for use with previously partially formed resistor elements, or it may be carried out during the formation of the resistor element, as desired.

Other objects and advantages of this invention will become apparent from the following description, reference being had to the accompanying drawings, in which preferred methods of manufacture of a resistor are diagrammatically illustrated. The essential features of the invention will be summarized in the claims.

In the drawings, Fig. 1 is an elevation of a lamp, partially broken away to illustrate a resistor mounted therein; Fig. 2 is an enlarged perspective view of one form of resistor which may be made by the improved method of manufacture; Fig. 3 is a sectional view of a mold used in making the resistor shown in Fig. 2; Figs. 4, 5 and 6 are view-s similar to Fig. 3, but illustrating different steps of the improved method; Fig. 7 is a plan view of the mold of Figs. 3 to 6, inclusive, and illustrates a plurality of resistors with a conductor attached thereto; Fig. 8 is an enlarged sectional view of a resistor and diagrammatically illustrates a final step in the formation of the resistor; Fig. 9 is a fragmentary plan view of a modified form of mold; Figs. 10 to 13, inclusive, are sectional views of the mold shown in Fig. 9 as used in a somewhat modified form of method. of manufacture; Fig. 14 is a sectional View of "two resistors and illustrates the final steps of manufacture; Figs. 15 to 1'7 are so"- tional views similar to Figs. 10 to 13, but illustrating a different method of manufacture, and Fig. 18 is an enlarged perspective view of a resistor as made in accord with the diagrammatic illustrations of Figs. 10 to 17, inclusive.

For the most part, the lamp illustrated in the drawings is typical of a standard lamp construction now in general use. This lamp comprises a tubular glass envelope Ill into the base of which a header insert or electrode supporting element ll extends. A pair of electrodes (not shown) are secured to the top of lead wires I4 and I5 which extend through and are carried by the header insert. The header is tubular as shown in Fig. l, and is provided with a downwardly extending exhaust tube 16. This tube is axially aligned with the envelope l5 and extends some distance below the bottom of the header and envelope. The outer end !B of the tube i6 is initially open while the inner end is in communication with the interior of the envelope Ill. This enables the air to be exhausted from the envelope to form a partial vacuum therein, but after the vacuum is formed in the envelope, the lower end of the exhaust tube IB is sealed, as indicated at l8.

Secured to the envelop [0, as by cement l3, and enclosing the tube, is a metallic contactor base 20. The lead Wire l4 extends from the header through a contactor 2! carried by the base and is secured thereto, as by soldering. The other lead wire 15 is secured to a conductor 22 of an annular resistor 23 which encircles the tube immediately below the base of the envelope. A second conductor 24 has one end thereof secured to the annular resistor 23 in a region substantially diametrically opposite the conductor 22 and has its other end secured to the shell of the base 20, as by a soldered connection indicated at 26.

One form of resistor is illustrated in Fig. 2 and comp-rises an annular ring 23 of carbonaceous material. The conductors 22 and 24 comprise relatively short wires, one end of which is secured to the resistor by cement 2'! of a type which of itself is a conductor of electrical energy. Electrical resistors of this type are generally formed by molding a carbonaceous powder, including a thermo-setting binder. This powder is placed in a mold and compacted by pressure, then heated under pressure to cause the binder to set or form the material into a permanent shape. The resistors illustrated are particularly adapted for use in lamp assemblies and, therefore, are ring shaped to embrace the exhaust tube of the lamp, as heretofore described.

My improved method contemplates positioning a plurality of the rings 23 in cavities 39 of a mold as illustrated in Fig. 7. The mold cavities are aligned in the mold so as to provide both lengthwise and crosswise rows. After the resistor rings 23 have been positioned in the mold, a conductor wire Ed is stretched across the rows of resistors as illustrated in Figs. 6 and '7. The mold is provided with suitable pegs 32 about which the wire may be drawn or bent to guide it from one row to another. These pegs accurately align the wire so that it passes diametrically across each resistor. After the wire has been positioned and its loose ends secured to the endmost pegs as indicated at a cement 36 is applied to the wire in the regions where it contacts the resistors. This cement 35, as will be seen in Figs. 6 and "I, is applied at two places on each resistor.

One cement which has been found to be suit able for this purpose comprises a mixture of a water soluble thermo-setting resin and flake graphite. I have found that a mixture in the proportion of from one hundred fifty "(150) to four hundred (400) parts of flake graphite, to six hunderd (600) parts of resin provides a satisfactory cement. The preferred proportion, however, is two hundred twenty-four (224) parts of graphite to six hundred (600') parts of resin.

In using the cement, a paste is made by adding to the ingredients aforesaid a suitable liquid, such as water, alcohol or acetate carrier. The paste is brushed on the wires while they are stretched across the resistors, as indicated in Fig. 6, and is then air dried and subsequently baked at a temperature of about 325 F. for about twenty (20) minutes. The baking operation assures an efficient bond between the cement and carbon resister 23 as it drives all the moisture out of both the resistor and the cement.

After the conducting wire has been secured in position on the resistor by the baking operation, the units are severed from each other. This may be accomplished by passing a cutter or knife across themold and transversely of the wires, as indicated by the arrow in Fig. '7. Following the severing of the resistors from each'other, that portion M of the wires which bridges the central opening in the resistor fil is severed. This may comprise a mere severing of the wires, or it may comprise the removal of the central sections 6| as indicated in Fig. 8. This method of forming and attaching the conductor wires to the resistor is highly economical and insures accurate positioning of the conductor with respect to the resister.

While the resistor rings 23 may be preformedprior to placing them in the mold, it is obvious that partially formed rings of the carbonaceous powder may be placed directly in the mold cavities and the resistor may be formed by embedding the wire therein. A mold suitable for this purpose is shown in Figs. 9 to 1'7. Figs. 4 to 6 diagramatically illustrate a method wherein the resistor ring is partially formed (merely compressed) prior to being placed in the mold, whereas Figs. 10 to 13 illustrate a method wherein the carbonaceous powder itself is placed in the mold,

the wire is applied, and thereafter the assembly is subjected to heat and pressure.

The mold 45 shown in Figs. 10 to 13 is provided with aligned annular cavities which are intersected by a' slot 46 which extends into the mold to a depth slightly over half the depth of the cavities 41. Carbonaceous material in the form of a powder is then placed in the cavities ll as indicated in Fig. 12, and a continuous wire 46 is positioned in the slot 46. This wire extends through all of the cavities so that a single strand of wire may be used for all of the resistors in the mold. After the wire is positioned, a second mold member 38, illustrated in Fig. 13, is pressed into contact with the mold 45. The mold section d8 has annular formations which enter the annular cavities ll to compress the powder therein. Heat is then applied to the compressed units to set the resistors in the desired form. After the resistors have been heated suificiently, they are removed from th mold, and the wires are severed intermediate each resistor as indicated at 58, Fig. 14. The portion 51 of the wire within each resist-or is then severed or removed, as heretofore described, thus providing a resistor having a pair of conducting wires at diametrically opposite regions of the annulus.

A modification of the method is'shown in Figs. 15 and 16. As there shown, the resistor elements used comprise wafers which are partially compressed, being slightly greater than half the desired thickness of the resistor. One wafer is placed in each mold cavity 51. The wire M is then placed in the slot 36 atop the wafers, and a second wafer 53 is placed in the cavity on top of the wire. Heat and pressure are then applied, as heretofore described in connection with Fig. 13, thus securing and compacting the two resistor sections 52 and 53 together as an integral unit with the wire passing therebetween. The resistor elements are then removed from the mold and the wires are severed as heretofore described.-

If desired, the wafers 52 and 53 may be entirely preformed and a layer of cement may be applied to the resistors 52 prior to the application of the wire, and then the resistor elements 53 may be placed thereon and heat applied to bake the two together and to cause the cement to secure the two wafers together.

From the foregoing description, it will be seen that I have provided a very simple method of manufacturing resistors economically and 'effi ciently and that I have also provided an economical and efiicient manner of attaching electrical conductors to the resistor in a manner that permits accurate location of the conductors.

I claim:

l. The method of making electrical resistors, comprising placing a conductor across a row of resistor elements, securing the conductor to each element at two spaced regions, and thereafter severing the conductor intermediate the ole ments, and also intermediate said regions thereby to provide each element with a pair of spaced conductors,

2. The method of making electrical resistors, comprising placing a wire across a row of carbonaceous elements, securin the wire to and in electrical contact with each element at two spaced regions, and thereafter severing the wire between adjacent elements and removing a section of the wire intermediate said regions.

3. The method of making electrical resistors, comprising aligning a plurality of rings of carbonaceous material in a diametric row, laying an electrical conductor wire across the row of rings, securing the wire to each ring in the row, at diametric regions thereof, severing the wire intermediate each ring and severing the wire within each ring.

4. The method of making electrical resistors, comprising placing rings of carbonaceous material in alignment in two directions, laying a conductor wire diametrically across the rings in one direction, cementing the wire to and in electrical contact with the rings at diametrically spaced regions thereof, and thereafter severing the wire intermediate the rings and intermediate said regions.

5. The method of making electrical resistors, comprising forming a plurality of rings of carbonaceous material, aligning said rings in lengthwise and transverse rows, laying a conductor wire across all of said rings, said wire extending continuously across each lengthwise row and from each row to the next row, cementing the wire to each ring with a carbonaceous cement at diametrically spaced regions, applying heat to cure the cement, subsequently severing the wire between each transverse row of rings and severing the wire between the region of attachment to each ring thereby forming a plurality of annular resistors each having a pair of separate conductor wires.

6. The method of making electrical resistors, comprising forming a ring of carbonaceous thermo-settable material, placing the rings in rows in a mold, extending a wire diametrically across the rings and along the face of the mold, applying pressure and heat to the rings to set the material, and subsequently severing the wire intermediate adjacent rings and adjacent the axial center of each ring.

7. The method of making electrical resistors, comprising laying a wire in a longitudinal slot in the face of a mold having an annular reces intersected by the slot and extending into the mold a greater distance than the slot, filling said recess with a carbonaceous powder, applying heat and pressure to the powder to compact and set the same, and embed the wire therein, and finally severing the wire substantially at the center of each annulus.

8. The method of making electrical resistors, comprising forming a plurality of rings of carbonaceous material, laying a conductor wire diametrically across one of said rings, placing a second ring atop of said wire, securing the two rings together and to the wire, and finally severing the wire at the axis of the ring.

9. The method of making electrical resistors, comprising laying a wire in longitudinal slot in the face of a mold having a plurality of annular recesses diametrically intersected by the slot and extending into the mold a greater distance than the slot, filling each recess with a thermo-settable carbonaceous material, applying pressure to the material to compact the same and embed the wire therein, thereafter applying heat and pressure to the compacted material to set the same, severing the wire between each annulus so formed, and also severing the wire substantially at the center of each annulus.

10. The method of making electrical resistors, comprising pressing a carbonaceous thermosettable powder into rings, diametrically aligning a plurality of said pressed rings, laying a wire diametrically across all of said rings, positioning other pressed rings above the wire and in axial alignment with each of the first named rings, applying pressure to said units to compress them and embed the Wire therein, then applying heat to set the superposed rings into individual units each comprising a ring having a wire extending diametrically therethrough and thereafter severing the wire between each ring and also severing it between the points of attachment of the wire to each ring.

LESTER L. STOFFEL. 

